Avoid JS error when not on current day

app/views/conferences/show.html.erb

@@ -80,6 +80,10 @@ current_time = Time.zone.now.in_time_zone(@conference.time_zone)
             const pixelsPerHour = <%= pixels_per_hour %>;
             const currentTimeDiv = document.querySelector('#<%= date.strftime('day-%Y-%m-%d') %> .current-time');
 
+            if (!currentTimeDiv) {
+              return;
+            }
+
             if (
               currentTime.toDateString() === timelineStartsAt.toDateString() &&
               currentTime >= timelineStartsAt &&